This invention relates to an artificial knee prosthesis, or a prosthetic knee, for the replacement of a natural knee through surgical implantation.
In general, a natural knee is formed by the two condyles of the bottom part of the femur, the lower surfaces of which bear upon the complementarily shaped upper surface plateaus of the tibia through the intermediary of meniscii, a fibro-cartilage. Connection through the knee is provided by means of ligaments which also provide joint stability and help to absorb stresses applied to the knee. The femur, meniscii and tibia are normally subjected to relatively large forces in the course of supporting the major portion of a person's body weight.
Movement of the normal knee is complex, that is it is not simply a pivotal or rotational movement. Rather, a healthy, natural knee has the ability to move in four distinct manners. First, the natural knee joint permits flexion and extension between the femur and the tibia through an arc of about 135.degree.. This motion is a combined rotational, rocking and gliding movement of successive points of the femoral condyles and the tibial plateaus. Secondly, the healthy, natural knee permits a relative rotational movement between the condyles and the tibial plateaus. Thirdly, the knee permits some limited relatively sliding motion which might be described as taking place in a generally horizontal plane between the condyles and the plateau; and fourthly the knee permits a rolling-type motion, frequently referred to as abduction and adduction, between the condyles and the plateaus which might best be described as a limited rocking-type motion in a lateral direction, that is generally perpendicular to the plane in which the knee most commonly articulates (flexion and extension).
Aside from the proper geometric configuration of the condyles and the tibial plateaus, an effective, free movement of a natural knee in these four directions requires the presence of a fibro-cartilage, commonly referred to as meniscus, between the condyles and the plateaus. When the meniscii become damaged, deceased or inflammed, they cease to function properly, the mobility of the knee joint becomes increasingly impaired and movements are accompanied by increasingly severe pains.
To alleviate this condition, it is sometimes necessary to replace the natural knee by surgically implanting a prosthetic knee.